Serious reporting deficiencies exist in minimal important difference studies: current state and suggestions for improvement

BACKGROUND AND OBJECTIVES: To evaluate reporting of minimal important difference (MID) estimates using anchor-based methods for patient-reported outcome measures (PROMs), and the association with reporting deficiencies on their credibility. METHODS: Systematic survey of primary studies empirically estimating MIDs. We searched Medline, EMBASE, PsycINFO, and the Patient-Reported Outcome and Quality of Life Instruments Database until October 2018. We evaluated study reporting, focusing on participants' demographics, intervention(s), characteristics of PROMs and anchors, and MID estimation method(s). We assessed the impact of reporting issues on credibility of MID estimates. RESULTS: In 585 studies reporting on 5,324 MID estimates for 526 distinct PROMs, authors frequently failed to adequately report key characteristics of PROMs and MIDs, including minimum and maximum values of PROM scale, measure of variability accompanying the MID estimate and number of participants included in the MID calculation. Across MID estimates (n = 5,324), the most serious reporting issues impacting credibility included infrequent reporting of the correlation between the anchor and PROM (66%), inadequate details to judge precision of MID point estimate (13%), and insufficient information about the threshold used to ascertain MIDs (16%). CONCLUSION: Serious issues of incomplete reporting in the MID literature threaten the optimal use of MID estimates to inform the magnitude of effects of interventions on PROMs.